Many mobile machines, such as off-highway mining trucks, loaders, motor graders, material handlers and hydraulic excavators, include numerous moving parts that require proper lubrication to prevent premature failure. Critical areas may include, for example, wheel bearings, articulation joints and linkage joints. In many applications, these critical areas must be frequently lubricated, e.g. it may be desirable to lubricate as frequently as every 5-10 minutes.
To address this need, various automatic systems have been developed to provide lubrication during machine operation. Generally, such lubrication systems include a reservoir for lubricating material, a pump, supply lines, and one or more injectors arranged to deliver lubricant through feed lines to each of the lubrication points.
One of the difficulties associated with these systems lies in monitoring the amount of lubricant within the reservoir. In one respect, if the system runs out of lubricant, the critical areas are not receiving the necessary lubrication, which may result in premature wear or damage to the machine. Accordingly, the operator needs to be able to monitor the lubricant level, preferably during ordinary machine operations, from the machine operator station.
The lubricants typically employed in connection with such systems are extremely viscous, which makes many traditional level sensors used, for example, in connection with gas tanks, unworkable in connection with these systems. For instance, known in the art of level sensing are float-type sensors that include a magnet carried in a float assembly that rises and falls with the fluid level to open and close various magnetically activated reed-switches located at different axial positions along a vertically extending electrical circuit. One such fuel level sensor is described in U.S. Pat. No. 6,571,626 to Herford. However, due to the viscosity of lubricants such as those used in the above-described systems, such a float would be quickly rendered immobile and inoperative.
One reservoir with a level sensor that has been previously employed in connection with known lubrication systems is shown in FIG. 9. The reservoir 1 generally includes a refill connection 2, a vent conduit 4 connected to a vent line 6 above the reservoir 1, a pump conduit 8 fluidly connected to a pump 10 positioned above the reservoir 1, and a follower plate 12 within the reservoir 1 inner cavity 14.
One of the problems due to high viscosity of the lubricant is that the lubricant tends to stick to the sides and form clumps and voids within the reservoir. One of the results of this is that while there may be plenty of lubricant in the tank, it fails to be taken up by the pump conduit 8. The weighted follower plate 12 has been adopted to address this problem by forcing the lubricant downward so that it fills the lower cavity 22 below the follower, where it can readily be taken up by the pump conduit 8. However, the follower plate 12 places additional constraints on the type of level sensor that might be employed.
One solution, again shown in FIG. 9, has been to attach a cable 16 to the follower plate 12, the other end being connected to a visual indicator 18 that includes a metal rod 20 which is pulled downward when the follower plate 12 reaches a predetermined position, indicating a low level of lubricant. During filling of the reservoir, when the plate 12 reaches the top of the reservoir 1, the rod 20 is forced upward into the full position. However, this system does not provide continuous level sensing, and requires that the operator or maintenance personnel be able to see the indicator 18. Depending on placement of the reservoir 1, this does not allow for monitoring of the lubricant level during, for example, operation of the machine, or during refill operations where a fill port is located some distance away from the reservoir 1. During refill operations, without being able to determine the level in the reservoir, the tank can be over-filled, causing lubricant to be expelled onto the machine and into the environment, creating an unsightly and potentially contaminating and hazardous condition.
The present disclosure is directed to overcoming one or more of the problems set forth above.